An X-ray CT apparatus includes an X-ray source and an X-ray detector, which are disposed interposing an object in an opposing manner. The X-ray detector includes multiple channels (M channels) of detection elements along a direction orthogonal to the longitudinal direction of a table-top, which is the direction of the body axis of the object.
While various types of X-ray detectors are available, a scintillation detector, which has potential for downsizing, is generally used for X-ray CT apparatuses. Each detection element of the scintillation detector includes a scintillator and a photosensor, such as a photodiode (PD). The scintillator absorbs X-rays that are collimated in a preceding stage, and generates fluorescence through the absorption. The PD converts the fluorescence into an electric signal and outputs the electric signal to a data acquisition system (DAS). That is, according to an X-ray CT apparatus, an X-ray beam is delivered in a fan shape to a section (hereafter, referred to as a “slice plane”) of the object from the X-ray source so that X-ray beams that have transmitted a certain slice plane of the object are converted into an electric signal for every detection element of the X-ray detector thereby allowing the acquisition of transmission data.
Further, compared to the above described single-slice X-ray CT apparatus, a multi-slice X-ray CT apparatus includes, besides M channels of detection elements, a multiple rows (N rows) of detection elements along the body axis of the object, in the X-ray detector. The X-ray detector of the multi-slice X-ray CT apparatus is configured as a two-dimensional detector for X-ray CT having M channels×N rows of detection elements in total.
FIG. 9 is a side view showing an outline of the configuration of the periphery of an X-ray detector and a DAS in a conventional X-ray CT apparatus.
FIG. 9 shows an X-ray detector (a scintillation detector) 61, a DAS 62, a thermal shield 63 and a heater 64 which are disposed between the X-ray detector 61 and the DAS 62, and cooling fans 65a and 65b which are disposed in the periphery of the X-ray detector 61 and the DAS 62, in a conventional X-ray CT apparatus. As shown in FIG. 9, the X-ray detector 61 includes a collimator (N collimators corresponding to N rows) 71 which collimates the X ray that has transmitted an object, a detection element (N detection elements corresponding to N rows) 72 which generates an electric signal based on the X ray in a subsequent stage of the collimator 71. The detection element 72 is made up of a scintillator (N scintillators) 81 and a PD (a photodiode array (PDA) having N PDs) 82. The DAS 62, which is disposed in a subsequent stage of the PD 82, converts and amplifies the electric signal of the PD 82 into a voltage signal.
The collimator 71 and the detection element 72, which make up the X-ray detector 51, are configured as one body and are thermally shielded from the DAS 62, in which temperature significantly fluctuates, via a thermal shield 63 to keep the detection element 72, particularly the PD 82, at a constant temperature. Alternatively, the collimator 71 and the detection element 72 are configured as one body and are accommodated in a case as the thermal shield 63 to keep the detection element 72 at a constant temperature. Then, temperature control of the detection element 72 is performed by heating the detection element 72, which has no effect on the temperature fluctuation of the DAS 62, with the heater 64 of about 100 to about 150 [W] and also cooling the detection element 72 with the cooling fan 65a. The temperature of the detection element 72 is controlled, for example, in a range of 40±1 [° C.] which is higher than the room temperature, with the heater 64 and the cooling fan 65a. It is possible to maintain the image quality of CT images by controlling the temperature of the detection element 72.
On the other hand, in some cases, the substrate temperature of the DAS 62 rises to about 60 to about 90 [° C.] due to generated heat, leading to a malfunction of the DAS 62. In order to prevent an excessive temperature rise of the DAS 62, a cooling fan 65b for cooling the DAS 62 is attached to the substrate of the DAS 62. Thus, it is configured such that there is no excessive temperature rise in the DAS 62.
As so far described, in order to control the temperature of the X-ray detector 50, while the thermal shield 63 is used to shield exhaust heat of the DAS 62, heating equipment is provided on the side of the detection element 72 and, at the same time, cooling equipment is provided on the side of the DAS 62.
Thus, the conventional X-ray CT apparatus causes a waste of electric power in that, on one hand, heating of the detection element is performed while shielding exhaust heat of the DAS and, on the other hand, cooling of the detection element is performed in order to control the temperature of the detection element of the X-ray detector.
Moreover, as the DAS becomes more highly integrated and thereby downsized in recent years, it is required from a viewpoint of performance enhancement that the X-ray detector and the DAS are installed adjacent to each other. As an extreme of this configuration, it is conceivable that the X-ray detector and the DAS are configured to be a unitary structure (a modular structure). However, if a thermal shield is not installed in the conventional X-ray CT apparatus, the exhaust heat of the DAS will directly affect the temperature of the detection element making it difficult to keep the detection element at a constant temperature. Thus, since installing a thermal shield is a necessity in the conventional X-ray CT apparatus, it is difficult to achieve a unitary structure of the X-ray detector and the DAS. Further, if no heater is installed in the conventional X-ray CT apparatus, it cannot be expected that the temperature of the detection element is hematothermal. Thus, since installing a heater is a necessity in a conventional X-ray CT apparatus, it is difficult to achieve a unitary structure of the X-ray detector and the DAS.
In addition, disposing a heater in the vicinity of the X-ray detector may result in an ill effect that the heater acts as a noise source.